Fluid Inlet Temperature Research Articles

LSTM-BP neural network analysis on solid-liquid phase change in a multi-channel thermal storage tank

Latent heat thermal storage (LHTS) system is a crucial technology for achieving carbon neutrality and alleviating energy stress. Although metal foam can ameliorate the thermal storage rate of the LHTS system, the impact of the inlet velocity and temperature of heat transfer fluid (HTF) on the phase transition of phase change material (PCM) needs to be properly designed to achieve optimal performance. A novel multi-channel LHTS tank with metal foam is designed. A three-dimensional numerical model is established to describe the transient melting process in the LHTS tank. Besides, a new LSTM-BP neural network is developed, in which the HTF inlet velocity, temperature and time are employed as input data. Simulated results are consistent with the previous measurement data, verifying the correctness of the numerical methods. Results suggest that the whole melting time of the PCM is diminishing with increasing HTF velocity (or temperature). The machine learning prediction results show minor differences with the simulation results. The developed machine learning model provides new adaptive approaches for thermal storage design and operation.

Analysis and optimization of flow and heat transfer performance of active thermal protection channel for hypersonic aircraft

This paper presents a numerical simulation on the thermal–hydraulic performance of multiple parallel cooling channels to realize active thermal protection of hypersonic aircraft. The fluid velocity is set in the range of 0.5–2.5 m/s, with the corresponding Reynolds number of 4300 to 22,000, and results show that the rectangular and triangular channel have the best cooling performance on outer wall and inner wall with water as coolant, respectively. Further, “Diamond” channel is proposed to improve the cooling performance, and aviation kerosene RP–3 is used as coolant. Three inlet temperatures (243, 253 and 263 K) are applied to investigate the thermal protection performance of Diamond channel. The cooling performance of RP–3 is better than water, and total pump power of RP–3 is only 60% of water. It is found that the conspicuous symmetric longitudinal swirls generated at the leading edge effectively enhance the heat convection performance. Under the studied ranges of fluid velocity and inlet temperatures, outer and inner wall temperatures can be controlled below 700 K and 330 K, respectively. Subsequently, the preliminary parameters of the “Diamond” are investigated and optimized. Model with L = 16 mm, Yc = 3 and X = 8.8 mm has better thermal protection performance and mechanical properties.

Experimental evaluation of a new mini square channel air-cooled heat exchanger for an absorption chiller

• An air-cooled subcooler for absorption cooling systems is experimentally evaluated. • Square minichannels of 2 mm side and 11 cm length and natural or forced air are used. • Approach temperature, pressure drops and heat transfer parameters are obtained. • Correlations are derived for heat transfer and pressure drop in the subcooler. • A notable increase in the cooling power of the absorption system is obtained. A mini square channel air-cooled heat exchanger, operating as subcooler in the typical temperature range of absorption cooling systems, is experimentally evaluated. Working fluid flows along 82 square minichannels of 2 mm side and 11 cm length, manufactured on stainless-steel. Hot fluid flows downward through the channels and two cases are evaluated: natural and forced air convection. In the last case, ambient air flows in the upward direction. Two additional operating parameters are modified: the inlet fluid temperature, between 34.8 and 75.4 °C and the fluid mass flow rate, in the range from 5.7 to 29.1 kg/h. Inlet and outlet temperature and pressure for the fluid and ambient temperature are measured, while the air velocity is kept constant at 0.75 m/s. Results obtained for the approach temperature, pressure drops, heat transferred and heat transfer coefficients for the air-cooled subcooler are provided. Correlations are derived to predict the heat transfer coefficient and pressure drop of the subcooler. Integration of the air-cooled subcooler in a single-effect absorption cooling system is evaluated, showing a notable increase in the cooling power mainly in the case of using forced air flow.

A Thermal-hydraulic assessment of condensing tube bank heat exchangers for heat and water recovery from flue gas

Condensing heat exchangers are capable of recovering a significant amount of latent heat at temperatures below 100 °C from the flue gas of combustion-based heating systems due to the presence of water vapor in their exhaust streams. However, the condensation of acids along with water vapor creates a highly-corrosive environment in these heat exchangers. As such, a large majority of these heat exchangers are made from corrosion-resistant alloys, such as stainless steel. Polymer-based materials are cost-effective and have great corrosion-resistant properties. Since the performance parameters of a heat and water recovery unit depend on the size and compactness of their heat exchangers, it is challenging to compare the overall performance of stainless-steel condensing heat exchangers with polymeric ones based on the data available in the literature. The main goal of the present study is to develop and assess the thermal–hydraulic performance of a proof-of-concept condensing heat exchanger made of fluorinated ethylene propylene compared to the same condensing heat exchanger made of stainless steel for heat and water recovery from flue gas. For this purpose, an in-depth parametric study is conducted experimentally to evaluate the water recovery efficiency, total heat recovery rate, and pressure drop in the flow paths. The results revealed that the water recovery efficiency of the unit with a specific size, declines when the mass flow rate of the gas increases, although it enhances the total heat recovery of the unit. Moreover, increasing the volumetric flow rate of the heat transfer fluid flow slightly increases the total heat recovery of the stainless-steel condensing heat exchanger, but has a negligible impact on the total heat recovery rate of the polymer-based heat exchanger. Increasing the humidity ratio of the flue gas or the inlet temperature of heat transfer fluid does not have any significant effect on the flue gas pressure drop. These findings are significantly important and novel as they unlock the potential of using polymer-based materials with thermally conductive additives for latent heat recovery from flue gas.

Study on effect of tank and fin configurations and operating conditions on performance of thermal storage system

The low thermal conductivity of phase change materials (PCMs) is a crucial challenge in utilizing latent heat thermal energy storage (LHTES) systems. Incorporating fins into LHTES system is an effective approach to overcoming the low thermal conductivity of PCM and enhancing its performance. In the present study, computational fluid dynamics is used to investigate the effects of fin configurations and operating conditions on the performance of a shell-and-tube system assisted by fins. The heat transfer rate and liquid fraction are investigated to evaluate the thermal behavior of the proposed system. The enthalpy–porosity technique is employed to simulate the phase change. The temperature variations over time at different PCM locations are calculated and compared with the measured temperatures. The predicted results show that the fin thickness and the inlet temperature of the heat transfer fluid play a key role in reducing the melting and solidification time. The obtained results indicated that by increasing the fin thickness from 0.5 to 1 mm, the heat transfer rate increased by approximately 17%. Also, increasing the inlet temperature from 60 °C to 65 °C improved the heat transfer rate by 36.2%.

Single-Phase Dielectric Fluid Thermal Management for Power-Dense Automotive Power Electronics

This article describes the design and performance of a dielectric fluid cooling concept for automotive power electronics. The concept combines a low-thermal-resistance package (which eliminates metalized ceramic substrates) with a high-performance convective cooling strategy (slot jets impinging on finned surfaces). Modeling was first used to design the cooling system to maximize thermal performance and minimize pumping power. A prototype was then fabricated, and experiments were conducted to validate the model predictions using three fluids at various fluid flow rates (16.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s [1 L/min] to 68.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s [4.1 L/min]) and inlet temperatures (30 °C and 70 °C). The final design was compact (120-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> total volume, including heat exchanger and conceptual power modules) and cooled 12 devices (e.g., silicon carbide [SiC]). The validated model was then used to predict the junction-to-fluid thermal resistance and pumping power for various conditions, including −40 °C fluid temperature. The results predict thermal resistance values as low as 19 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·K/W is possible using the dielectric fluid cooling approach. The dielectric fluid cooling system is predicted to provide thermal resistance and pumping power values that are approximately 56% and 90% lower, respectively, compared to an automotive power electronics cooling system. Moreover, the dielectric fluids can be used for direct cooling of the bus bars, which can be an effective capacitor and gate driver cooling strategy and enable the use of new driveline fluids tailored for this application.

Energy pile groups for thermal energy storage in unsaturated soils

• Energy pile groups provide superior thermal energy storage performance over boreholes. • Both energy pile geometry and number of internal heat exchangers are important. • Lower thermal conductivity of unsaturated soils leads to higher heat retention. • Transient decreases in degree of saturation were observed over several years. • Heat transfer in unsaturated soil can be enhanced in some cases via vapor diffusion. A coupled heat transfer and water flow model implemented in COMSOL and validated against measurements from a tank scale test was applied to investigate the application of energy pile groups for thermal energy storage in unsaturated soil layers. The novel focus of the investigation was understanding the long-term thermo-hydraulic response of the unsaturated soil within the energy pile group during heat injection at high temperature up to 90 °C and associated impacts on the heat storage performance. Unsaturated soil layers are advantageous for thermal energy storage due to enhanced convective heat transfer during injection associated with vapor diffusion and favorable insulation properties during storage associated with lower thermal conductivity of soils surrounding a heat storage system. Evolutions in temperature and degree of saturation in soil layers having different hydraulic properties and water table depths were simulated during five years of operating a group of five energy piles with inlet fluid temperatures of 90 °C during heat injection and 30 °C during heat extraction. Transient fluctuations in the degree of saturation were observed in all soil layers simulated, but a permanent decrease was only observed for a soil layer having a greater air entry suction after several cycles of heating and cooling. While the heat storage in energy pile groups in unsaturated soil layers was always between that of dry and saturated soils with no groundwater flow, the soil hydraulic properties and water table depth were found to control both the rate of heat transfer and the total heat stored. When comparing the performance of energy pile groups with a group of borehole heat exchangers commonly used in heat storage applications, the energy piles were approximately 1.2 times more effective in extracting heat with a faster response confirming their suitability for heat storage.

Numerically analysis of a Phase-change Material in concentric double-pipe helical coil with turbulent flow as thermal storage unit in solar water heaters

This research investigates a 3-D double-pipe helical coil heat exchanger containing Phase-Change Material (PCM) as a thermal storage system in solar water heaters. A concentric double-pipe follows the helical profile upward and creates a heat storage unit. In the unit, water in turbulent mode flows in the inner pipe as a Heat Transfer Fluid (HTF), and RT-50 is considered PCM placed in the annulus. This heat exchanger with all related conditions is modeled in Ansys Fluent 19 software, and we used the k-ε RNG turbulence model to simulate turbulent flow. For evaluating this novel model of thermal storage unit, the impact of some critical geometrical parameters, like helical pitch, inner and outer pipe diameter, and some flow parameters, such as fluid inlet temperature and Reynolds number, have been analyzed. The most important outcomes of the investigation show that inlet temperature and inner and outer pipe diameter are critical factors for the storage system's design. A 1.5 % change in inlet temperature will enhance the melting rate by 27 %. Also, by increasing the inner pipe diameter by 42 %, the melting process was improved by 92 %, while the outer pipe diameter was inversely related to the melting rate. A 20 % increase in this parameter's value showed a 52 % reduction in the melting. Moreover, the change in the helical pitch could not significantly affect the PCM melting process, and for a 300 % increase in pitch size, the melting process increases only by 0.6 %.

Performance investigation of latent heat energy storage in series and parallel arrangement: A numerical study

Latent heat storage is a prolific technology to ensure a continuous heat supply. Charging and discharging plays a vital role in deciding the overall performance of the storage system. In the case of multiple units of latent heat storage, the storage performance depends on the type of heat exchanger connection (series/parallel), heat-carrying fluid passage, and flow parameters. The rectangular shell and tube heat exchanger are selected to investigate the effect of connection and flow parameters during the charging and discharging. The series and parallel connection of rectangular shell and tube heat exchanger filled with phase change material RT35 is simulated for charging and discharging in ANSYS FLUENT. The heat-carrying fluid's temperature and flow rate are varied to report the effect of flow parameters. The inlet temperature of heat-carrying fluid water is kept at 80 °C and 60 °C, while the flow rate ranges from 0.6 LPM to 1 LPM. The results indicate that the series arrangement is better than the parallel arrangement in all flow conditions in both charging and discharging cycles. For series and parallel connection, when the flow rate increases from 0.6 LPM to 1 LPM, melting time reduces up to 24 % and solidification time up to 30 %. Moreover, charging gets affected by the inlet temperature of heat transfer fluid, a 42 % increase in melting time is observed when inlet temperature is reduced from 80 °C to 60 °C.

Study on temperature drop and cooling effect of cold wall for backfill body with embedded cold fluid tube

In recent years, the thermal damage in deep mine has become an urgent problem to be solved. A three-dimensional heat transfer model of backfill body with embedded cold fluid tube was established, the influence of tube spacing, the inlet temperature and velocity of cold fluid and the thermal conductivity of backfill body on the temperature distribution and cooling capacity of cold wall were analyzed. The results show the cooling capacity at steady deceases from 11.72 kW to 4.16 kW when tube spacing increases from 0.5 m to 1.5 m, the cooling capacity increases by 2.06 kW when inlet temperature decreases by 4 °C. When thermal conductivity increases from 0.5 W/(m•°C) to 2.0 W/(m•°C) in 0.5 W/(m•°C) increment, the increment of cooling capacity is about 3.22 kW, 2.17 kW and 1.52 kW successively on average in 20 days–60 days. Comparison shows the wall temperature of backfill body obviously decreases and quickly forms the cold wall as cold fluid passing through tube, the cold will be released rapidly from cold wall to airflow. The research can provide the theoretical basis for the application of radiation cooling of backfill body in the control of mine thermal damage.

Numerical investigation and modelling of controllable parameters on the photovoltaic thermal collector efficiency in semi-humid climatic conditions

ABSTRACT Hybrid Photovoltaic Thermal (PV/T) systems are energy-generation systems that transform thermal irradiance into both electrical and thermal energy at the same time. Hybrid photovoltaic thermal systems consist of a photovoltaic panel connected to a thermal collector. The main objective of this paper is to find the optimal operating conditions that can be controlled to decrease the photovoltaic panel temperature in order to improve the electrical and thermal performance of PV/T systems. In this work, we proposed the 3D numerical model that is implemented within the COMSOL Multiphysics program to study the PV/T system. The experimental input data being used in this research study reflects a typical Algerian area with semi-humid climate conditions. We study the effect of water velocity, pipe length, diameter, thickness and inlet fluid temperature on the electrical and thermal performance using the design of experiments (DOE) method. Further, the analysis of variance (ANOVA) is used to identify which of these effects impact the most the photovoltaic thermal and electrical efficiencies, the response surface methodology (RSM) is employed to describe how these effects are interacting. Based on ANOVA analysis, the following factors are reported to be important: water velocity, pipe diameter, pipe length and the inlet fluid temperature. Further, there is a significant interactions between water velocity, pipe length and pipe diameter. Among the operating conditions being calculated using the RSM, the optimal one is found when water velocity, pipe length, pipe diameter, pipe thickness and inlet water temperature have the following values, 0.05 m/s, 7.27 m, 0.01 m, 0.0008 m and 10°C, respectively. The corresponding thermal, electrical and overall efficiency were found around 80.73%, 12.87% and 93.60%, respectively. The proposed simulation model provides a reliable framework to study, improve and predict PV/T systems performance whilst ensuring low computational time.

Numerical study of high-temperature cascaded packed bed thermal energy storage system

The thermal energy storage system (TES) in the form of packed bed with encapsulated phase change materials (EPCMs) can further improve the thermal performance of ordinary TES. This study presents a numerical model for a three-dimensional cascaded packed bed thermal energy storage system (PBTES), in which an effective thermal conductivity model is used by consisering the natural convection effects in each EPCM based on its volume average liquid fraction. To examine the system-storage thermal energy and exergy in PBTES accurately, a thermodynamic analysis approach is also given. The high-temperature PCMs are grouped as KNO3, NaNO3, and NaNO2 according to the phase transition temperature from high to low in the packed bed stage. The effects of element stages on the thermal performance of PBTES are studied. Results show that the total thermal energy storage of cascaded-PBTES is 38.5% higher than that of single-PBTES (KNO3), and the total thermal exergy storage is 30.8% higher than single-PBTES. The average exergy efficiency possessed by cascaded-PBTES is 5% higher than that of single-PBTES. Furthermore, the effects of heat transfer fluid (HTF) inlet temperature and mass flow rate on the thermal performance of cascaded-PBTES are discussed. The increase of inlet temperature and mass flow rate can promote the charging process and influence the exergy efficiency. However, increasing the inlet mass flow rate will not lead to an increase in maximum thermal energy and exergy storage capacity.

Nusselt Number Prediction for Oil and Water in Solar Tubular Cavity Receivers

In this study, a numerical model was developed for prediction of Nusselt number in solar cavity receivers. Thermal oil and water were used as the working fluid. A dish concentrator with different shapes of the cavity receiver, including hemispherical, cylindrical, and cubical, was investigated. The different shapes of cavity receiver were studied under the same operating conditions for prediction of the internal heat transfer coefficient correlation for each cavity receiver. The system is investigated under the variation of solar radiation, flow rate, and inlet temperature of solar working fluids. The developed thermal model is validated based on the experimental data for the cylindrical cavity receiver using thermal oil. The results reveal that the hemispherical cavity receiver had the highest cavity heat gain, heat transfer coefficient, and Nusselt number values compared to two other cavity receivers. It could be concluded that the cavity heat gain, and heat transfer coefficient, and Nusselt number amounts had improved with increasing solar radiation, increasing flow rate, and decreasing inlet temperature of the working fluid. Some equations were suggested for prediction of Nusselt number with the variation of solar radiation, flow rate of the working fluid, and inlet temperature of working. It was concluded that application of thermal oil had resulted in higher Nusselt numbers than the use of water as the solar working fluid. Consequently, the application of oil is suggested for high-temperature systems.

Long-term dynamic heat transfer analysis for the borehole spacing planning of multiple deep borehole heat exchanger

In this paper, based on the heat transfer characteristics of deep borehole heat exchanger (DBHE), the superposition dimension reduction algorithm was used to solve the heat transfer model of multiple DBHE (MDBHE). Compared with the monitoring field data, the simulation results calculated by using the superposition dimension reduction algorithm are accurate and reliable. Meanwhile, its computation speed is 4 orders of magnitude faster than that of commercial software. This algorithm was also used to simulate the influences of borehole spacing on long-term heating performance of a DBHE composed of four boreholes, and the results were compared with a single-borehole DBHE, which indicate that increasing borehole spacing can effectively reduce the thermal disturbance among boreholes and enhance heat extraction capacity. When the borehole spacing among MDBHE increases to 50–60 m, the differences of inlet fluid temperature, soil temperature and borehole wall temperature between multiple and single DBHE are obviously reduced. Therefore, the superposition dimension reduction algorithm can quickly and efficiently solve the underground heat transfer problem of MDBHE, which can provide a fast calculation method and theoretical basis for engineering design of borehole spacing. It is recommended that borehole spacing to be 50–60 m if ground area is enough.

Experimental and numerical investigation of longitudinal and annular finned latent heat thermal energy storage unit

The melting process of phase change material (PCM) in horizontal latent heat thermal energy storage (LHTES) units with longitudinal and annular fins was experimentally studied under the same fin volume condition. The PCM melting time of the annular fin unit is reduced by 13.7% compared to that of the longitudinal fin unit. The annular fins are more responsive to the increase in heat transfer fluid (HTF) inlet temperature and the longitudinal fins are more responsive to the increase in HTF flow rate. After that, numerical studies were also performed for the two LHTES units to reveal in-depth the differences in heat storage processes. The results show that the longitudinal fins perform better in the early stage due to their larger contact area with the inner tube and a denser distribution near the inner tube. But it also limits the natural convection in the latter stage. The annular fins have better natural convection performance in the latter stage and therefore have better heat storage performance. Based on the analysis, a composite fin was designed to combine the advantages of longitudinal and annular fins. Numerical results show that the newly designed fin results in a 21.6% melting time reduction compared to the longitudinal fin model and a 9.5% melting time reduction compared to the annular fin model. Finally, two principles to guide the fin design in horizontal shell-and-tube LHTES units were summarized.

Exergetic Performance Analysis of Energy Storage Unit Fitted With Wire Coil Inserts

Abstract In a sensible storage system, energy is stored based on the distribution of energy and exergy at the specified conditions. It is believed that the least temperature gradient leads to a higher exergy availability and lower entropy generation in a storage system. An energy storage unit with multiple passages fitted with wire coil inserts is evaluated in the present work by assessing the exergy stored and the entropy generation number for heat transfer fluid (HTF) inlet temperature range of 45–75 °C and HTF flowrate of 0.022–0.029 kg/s. The wire coil inserts have a (p/d) ratio in the range of 0.25–0.75. The maximum exergy storage rate in the energy storage unit is found to be 55.43 W corresponding to an energy storage unit having wire coil insert (p/d = 0.25) at the HTF inlet temperature of 75 °C and HTF flowrate of 0.029 kg/s. Entropy generation number of the system with wire coil inserts (p/d = 0.5), compared to smooth HTF passage, is found to be 42.32% at HTF flowrate and inlet temperature of 0.026 kg/s and 45 °C, respectively.

Thermal Performance Analysis of a Linear Fresnel Concentrating Solar Collector Absorber Tube

Linear Fresnel solar collectors are suitable for a wide range of applications, which include steam generation for power generation, industrial process heat, solar cooling, institutional and domestic hot water production etc. The thermal performance of a linear Fresnel solar collector absorber tube was investigated in this study for different fluid mass flow rates, heat flux intensities, heat transfer fluid inlet temperatures, ambient air temperatures and external loss heat transfer rate. Turbulent flow liquid water heat transfer fluid and uniform circumferential heat flux distribution boundary were considered under steady-state conditions. The fluid flow was considered incompressible. This study was limited to a first order model approximation for thermal performance of a linear Fresnel solar collector absorber tube. The heat transfer fluid and absorber tube material properties were considered constant and independent of temperature. The results indicated that the absorber tube outlet heat transfer fluid temperature decreased with an increase in the Reynolds number and increased with the heat flux intensities. Thermal efficiency increased with an increase in the heat transfer fluid mass flow rate and however, decreased with increase in pressure drop and the consequent pumping power requirement. It was also found that the thermal efficiency of the collector decreased with an increase in the fluid bulk inlet temperature and decreased with an increase in the external loss heat transfer rate.

Comparison of Thermal Behavior of Self-Designed Internally Cooled Cutting Tool for Various Heat Transfer Fluids-Statistic and Computational Fluid Dynamics Approach

Abstract Compared with dry machining, using traditional cutting fluids has some weaknesses, such as environmental pollution, high machining costs, and harmful effects on human health. Internally cooled cutting tools (ICCTs) have been promising, sustainable, health-friendly, and green technologies for turning applications. However, the effects of different types of internal coolant fluids on insert tip temperature (Ttip) have not been investigated for ICCTs. The machining quality of metallic materials and tool life can improve with effective cooling. This study investigates the internal cooling performance of a self-designed internally cooled smart cutting tool (ICSCT) by comparing different heat transfer fluids. Therefore, a conjugate heat transfer (CHT) model was set for a self-designed ICSCT. The CHT simulation was experimentally confirmed using pure water (…developed by Ozturk, E., Yildizli, K., and Saglam, F., 2021, “Investigation on an Innovative Internally Cooled Smart Cutting Tool With the Built-In Cooling-Control System,” Arab. J. Sci. Eng., 46(3), pp. 2397–2411). After that, the effects of flow velocity (Vf) and the inlet temperature of the coolant fluid (Tinlet) alongside different types of glycol-based heat transfer fluids (including pure water) on Ttip were statistically evaluated by the Taguchi method and analysis of the variance (ANOVA). It was found that the most influential factor was the Tinlet at a contribution ratio level of 88.32%. Additionally, according to statistics, Vf and the type of heat transfer fluid were significant. Hence, since no external coolant is used, the designed smart tool can be considered environmentally friendly and health-friendly. In conclusion, glycol-based fluids can be a better choice for internally cooled tool designs owing to their superior features, e.g., corrosion prevention, nontoxicity, and stable heat transfer capability at lower temperatures compared to pure water, although pure water has better thermal properties than the glycol-based fluids (Dynalene Heat Transfer Fluids Technical Datasheets, Cited March 31, 2020).

Waste Heat Recovery from Air Using Porous Media and Conversion to Electricity

This paper presents a numerical study of waste heat recovery from a fluid stream using thermoelectric devices. The system consisted of a square section duct with spherical porous media placed in its central region. Hot air circulates continuously through the duct and exchanges energy with the solid matrix and subsequently with the thermoelectric modules. The mathematical model of the system was solved using ANSYS/FLUENT software, requiring the implementation of user-defined functions (UDFs) and user-defined scalars (UDS) regarding porous media and thermoelectric generation modelling. From the simulations carried out, global efficiency and electrical power values were obtained in the range of [0.11–4.51] [%] and [0.01–12.77] [W], respectively. Furthermore, for the set of variables analysed, it was observed that the performance of the system is favoured by an increase in the fluid inlet temperature and speed, as well as by a higher external heat transfer coefficient.

Flat-plate solar collector thermal performance assessment via energy, exergy and irreversibility analysis

This paper presents a detail exergy analysis of a flat-plate solar collector based on irreversibility rates. The governing equations of the flat-plate collector are obtained by writing energy and exergy conservation equations for glass cover, absorber plate and working fluid. The computed results of this study are in concordance with previous studies experimental data. Our findings reveal that 84.97% of total collector irreversibility are linked to the absorber plate. Increasing the flow rate to 0.0056 kg/s decreases the irreversibility rate in the absorber plate to a minimum of 579.20 W and increases the irreversibility rate in the working fluid to it maximum of 158.83 W. The maximum exergy efficiency was 33.21% for a flow rate of 0.0056 kg/s and inlet fluid temperature of 30 °C. An increase in inlet fluid temperature from 20 to 65 °C decreases the absorber plate irreversibility by 129.13 W, meanwhile the working fluid and glass cover irreversibility increase by 30.37 W and 99.39 W, respectively. An increase in number of absorber tube from one to sixteen increases the energy and exergy efficiencies respectively by 34.61% and 92.94%. Meanwhile the absorber plate irreversibility rate increases by 97.49% and the irreversibility rates of the working fluid and glass cover reduce by 72.06% and 89.01%, respectively.